1. Field of the Invention
The present invention relates to a coupling channel noise canceling circuit applicable to a portable terminal such as a European GSM (Global System for Mobile Communication) terminal, and more particularly, to a coupling channel noise canceling circuit that can cancel a noise due to coupling channel characteristics in operation by presetting the coupling channel characteristics that cause a noise due to an intermodulation between a communication signal of, for example, GSM and a broadcast signal of, for example, DVB-H (Digital Video Broadcasting-Handheld) or a noise due to an interference between communication signals.
2. Description of the Related Art
In a wireless communication field, the widespread use of portable phones is rapidly advancing a ubiquitous (mobile communication) society that can provide a free, world-wide communication service anytime, anywhere. Also, the development of a technology capable of transmitting a large amount of information as well as simple call data is rapidly advancing the integration of IT equipments including portable terminals, so that image and broadcast signals can also be viewed through portable terminals.
However, modules added in this integration process to provide various functions in portable terminals and IT equipments may cause interference noises on other modules. What is therefore required a technology of analyzing and canceling the influence of interference signals due to the modules added in the integration process.
Recently, as much attention is recently drawn to digital broadcasting, DMB (Digital Multimedia Broadcasting) technologies are being developed in Korean and DVB (Digital Video Broadcasting) technologies are being developed in Europe.
Examples of the DVB include DVB-T (Digital Video Broadcasting-Terrestrial) and DVB-H (Digital Video Broadcasting-Handheld). The DVB-T provides signal reception at a home or office stationary device from a broadcasting station, and the DVB-H considers the low power consumption, mobility and portability of portable phones or portable image devices.
When one terminal supports two or more functions (e.g., GSM/DVB-H) according to the integration of mobile terminals, an interference between modules may degrade the receive (RX) sensitivity of the modules. Various frequency components such as a DVB-H signal, DVB-T signal, a GSM-TX signal and a GSM-RX signal are applied to signals received by an antenna of a DVB-H receiver. A signal, which affects the DVB-H receiver most greatly among the received signals, is an interference noise due to an intermodulation between a DVB-T signal and a GSM-TX signal as illustrated in FIG. 1.
FIG. 1 is a diagram illustrating an interference noise due to an intermodulation between a DVB-T broadcast signal and a GSM-TX signal. Referring to FIG. 1, even when the frequency bands of an actual GSM-TX signal and DVB-T signal are different from a DVB-H RX frequency band, an intermodulation component of the two frequency components is generated within the DVB-H RX frequency band, so that it behaves as an interference noise signal stronger than a weak DVB-H signal, thus degrading the RX sensitivity of a DVB-H receiving module.
FIG. 2 is a diagram illustrating an interference noise due to a GSM-TX signal. Referring to FIG. 2, when a TX signal of a GSM terminal is transmitted, an interference signal due to a phase noise is generated very strongly in side-bands, in addition to a GSM-TX frequency. This interference signal is transmitted in a DVB-H RX band, thus degrading the RX sensitivity of the DVB-H. In actuality, an RX broadcast signal of a GSM/DVB-H terminal is a low-power signal of about −80 dBm or less, and it is necessary to deal with the performance degradation due to an interference signal of a GSM-TX signal higher than it. An interference signal cancellation of about −22 dB is necessary for improvement of the DVB-H RX sensitivity.
What is therefore required is a countermeasure against an interference noise due to an intermodulation between the RX frequency band of the DVB-H and the frequency band of the GSM-TX/DVB-T signal and an interference noise due to the GSM-TX signal.
A related art interference noise canceling technology uses a filter to cancel frequency bands except RX frequency bands in a receiver. This interference noise canceling technology, however, fails to efficiently cancel an interference noise present in the RX frequency band.